Clutch drive



C. P. PEPPER CLUTCH DRIVE Oct. 26, 1954 Filed March 17, 1950 y m m/Ma NA EP R W A P I- M.

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Patentecl Oct. 26, 1954 CLUTCH DRIVE Carl P. Pepper, Danville, Ind., assignor to The Marquette Metal Products Company, Cleveland, IOhio, a corporation of Ohio Application March 17, 1950, Serial No. 150,235

2 Claims.

This invention is illustrated as embodied in an already known type of automatic starter unit mechanism for internal combustion engines, such mechanism being designed for attachment to the drive shaft of an electric starter motor for crank ing the engine. The mechanism operates through mating screw elements automatically to move a starting pinion into mesh with a cooperating gear of the engine to crank it consequent upon energization of the motor and operates consequent upon starting of the engine and deenergization of the motor to cause the pinion to be moved out of mesh with such gear and be returned to its initial idle position.

In the operation of such starter mechanisms, as outlined above, it is desirable to provide an impositive torque transmitting connection be tween the pinion and the nearest associated screw element for torsional cushioning or shock absorption at the instant of engagement of the pinion with the cranking gear as well as when the pinion returns to its initial position. Such cushioning is accomplished in the illustrative constructicn hereof essentially as in that forming the subject of Schneider et al. Patent 2,481,248, September 6, 1949, namely, through the intermediary of an overrunning double drum, self-energizing helical spring clutch forming the impositive connection partly by reason of torsional yield in the spring through contraction of coils intermediate of the end Or energizing coils from relaxed position to full clutching position, and possibly through momentary slippage of the end coils on one or the other or both of the associated drums.

The amount of yield due to such slippage, as mentioned above, cannot be very reliably predlcted but, practically speaking, said amount can be maintained within safe operating limits if substantially uniform areas of contact between the end coils and the drums are maintained. In any event energization of the load carrying coils of the spring is thus assured. The present invention, indicating its principal object, is directed to a solution of the problem of maintaining substantially uniform contact areas, and at the same time avoiding maintenance of such close manufacturing tolerances between the various parts constituting the clutch as would make the same prohibitively expensive in high quantity production.

Other objects and features of the invention will be brought out and explained in the following description of an illustrative form.

The drawing, Fig. 1, shows partly in longitudinal central section and partly in elevation the starter unit assembly and cooperating engine parts; and Fig. 2, shows the improved clutch spring in side elevation, a few of the coils being shown broken away and sectionally.

In Fig. l, the armature shaft I of an electric starter motor 2, partially shown, extends from the motor through a housing 3, having a supporting bearing for the shaft at 4. Part of the usual flywheel gear 5 of the engine extends into the housing for engagement by the starter mechanism Ill, the pinion 6 of which is shown in its idle position. In its cranking position th pinion engages a stop collar l on the drive shaft.

Said starter mechanism Iii includes a sleeve 12 with external threads or helical splines 13. The sleeve l2 has an enlarged head It, the sleeve with its head and the shaft i being rigidly secured together against relative movement.

An internally screw threaded nut l5, slidably mating the threads or helical splines I 3, has driving clutch drum surfaces ll, ll of relatively different diameters, and a driven clutch drum member l6 coaxial with the nut, and partly journalled for free turning on it at stepped pilot shoulders l8, [8 has driven clutch drum surfaces I9, [9' of relatively different diameters paired with the surfaces ll, I7 and positioned reversely thereof.

The clutch drum surfaces H and I9 are fairly narrow cylindrical ribs on which a very few of the coils 2i and 23 (clutch energizing coils), at respective ends of clutch spring 22, bear continually through interference fitting or preloading of those coils 2| and 23 uniformly on the ribs. The intermediate (load carrying) coils 24, see Fig. normally clear the drum surfaces [1' and [9' in the illustrated relaxed condition of the coils 24 (starter mechanism inactive).

Through the friction coupling provided by the clutch spring and rib surfaces l1 and 19 the nut and driving clutch drum [5 is always torqueconnected to drum member It; and that member, in turn, is splined at 25 to the pinion 6, and provided with axially yielding jump spring means at 25' to facilitate meshing of the pinion and gear teeth prior to cranking, all as fully explained in the Schneider patent. As also explained therein, demeshing of the pinion and flywheel gear teeth occurs as a function of acceleration of the flywheel gear as the engine starts under its own power. To aid in the return of the nut and spring clutch assembly and pinion to the initial idle position or to hold it there against vibrational influence tending to displace it, a low rate coil spring 26 is suitably connected between parts l4 and Hi. The spring acts normally to hold a pair of lugs 21 and 28, on parts l4 and I5, in mutual abutment. The spring is deflected axially and torsionally when the pinion is moved to cranking position.

The nut and drum forming member |5 has a shoulder at 30 for abutment with one end of the clutch spring and the part IS, a shoulder 3 I, for abutment with the opposite end. Additionally the parts I5 and I6 are held together by a tubular case having inwardly flanged end portions so made as to allow said parts to turn freely relative to each other. The radially outermost mutually adjacent surfaces defining the stepped shoulders I8, I8 is usually referred to as the "crossover for the clutch spring for obvious reasons.

Referring further to the clutch spring 22, Fig. 2, said spring has all its coils closely wound except for one or two coils near one end as indicated by spaces 34. Those coils are spread apart (e. g. after being originally closely coiled or at any step in the manufacture of the spring, as during coiling) to an extent such that when the spring is assembled in place with the drums the spring ends which are preferably ground approximately flat always bear, axially of the assembly, on the respective shoulder surfaces 33 and 3|. Thereby if the shoulders 30 and 3| happen to be spaced apart farther than usual and the spring has been ground of slightly less length than usual, but within appropriate tolerance limits, the end coils 2| and 23 will nevertheless be so located as to preserve uniform total contact surfaces for energizing engagement with the drum (rib) surfaces ll and I9. Furthermore the clutch spring cannot be collapsed endwise into tight coil to coil engagement (preventing contraction of the intermediate load-carrying coils 24 against the drum surfaces IT and H) as could happen if all the coils were uniformly close-wound and the spring just filled the space between shoulders 30 and 3|, when assembled into place. Tolerances are compensated for by the axial yielding of the spring.

The reason it is preferred that the coils of the clutch spring generally be close-wound rather than with a slight space between all of them such as would prevent axial crowding during operation due to unfortunate choice of manufacturing limits is that open coiling makes the spring too flexible to be effectually and firmly held in the end grinding fixture used for quantity production for grinding of the spring ends. The present preferred solution enables the coils to be close wound so that the coiled blank is more nearly a solid metal cylinder. Spreading of the coils at 34 can be done in any suitable fixture arranged to maintain the end faces of the spring approximately parallel during spreading of the coils.

The illustrated spring stock used to form the clutch spring is known as high crown wire, reference being had to the curved clutching surfaces 35 thereof Fig. 2. Those, theoretically, make line contact with the clutch drum surfaces which is desirable in order to insure energization under all practical conditions (high unit pressure against the drum surfaces I1 and I9).

It will be readily understood that when the starter motor 2 is energized and the pinion 6 and gear 5 go into mesh there is a relatively high shock torque due to the rapidly revolving motor armature and the parts directly coupled to it and the not yet moving engine parts. The shock torque drops rapidly as static friction of the engine crankshaft, etc., assembly is overcome and the motor armature decelerates to cranking speed. The cushioning afforded by contraction of clutch spring coils 24 against the drum surfaces and I9 as the flywheel gear gets under way is usually suflicient to avoid damage to any part of the starter mechanism due to the shock loading. When that is not suflicient at the instant of pinion and gear tooth engagement and before the coils 24 are fully contracted the clutch spring coils 2| and 23 may slip momentarily on the clutching land surfaces l1 and I9 to afiord further cushioning. Since full clutching of all the coils necessary to deliver cranking torque requires that suflicient energizing friction be maintained notwithstanding inherent drop in friction coefficient due to the possible initial slippage it is highly important that the areas of contact between the energizing coils and their lands or drum surfaces I"! and I!) do not diminish beyond a critical amount. The open coiling as at space 34, by enabling the ends of the spring to be safely maintained against the shoulders 3|] and 3| under all circumstances, insures maintenance of the necessary areas of contact for contracting the load carrying coils 24 against their drum surfaces during the cranking operation.

The position of the open coiling (space or spaces 34) may vary; and the open coiling may be effected near both ends of the spring instead of at but one end.

The open coiling should begin a substantial distance from the active energizing coils 2| (or 23) as well as from the crossover or highest duty coils. The latter should, of course, have as much total clutching area as practicably obtainable.

When the engine starts and the starter pinion 6 is being thrown out of mesh with the accelerating fly-Wheel gear 5, by reverse screw action of the helical splines l3, there is some danger that the starter motor windings may be damaged by overspeeding. The spring clutch overruns to prevent such damage and one reason for the narrowness of the drum surfaces I! and I9 is to minimize overrunning drag. Overrun can also occur at the instant the lugs 21 and 28 ar brought together, so that shock torque is cushioned and rebound is prevented.

I claim:

1. An overrunning spring clutch assembly comprising two coaxial clutch drums of substantially equal diameter at their adjacent ends to provide main clutching surfaces, each being stepped so as to have another diameter portion at a distance from said ends to provide energizing clutching surfaces, the two drums having axial shoulders facing toward each other beyond the energizing surface portions in directions away from said ends, means mounting the drums for corrotation and relative angular movement while holding the shoulders an approximately fixed distance apart, and a helical clutch spring bridging the drums, with axially close-wound energizing coils tight on the energizing surfaces and having main clutching coils normally spaced from the associated main cutching surfaces but which can be caused to grip the main clutching surfaces through angular relative movement of the drums in the torque transmitting direction, characterized in that the spring, in a relaxed state is of a length greater than the distance between said shoulders and has at least two of its main clutching coils openly wound and thereby spaced apart relative to the spacing of the energizing coils a distance such that, with the spring ends in abutment with said shoulders, the spring is not completely collapsed endwise, whereby minor manuenergizing coil portions from the region of the facturing errors in forming the spring as to length spring which lies radially opposite the two muor in forming the drums as to the spacing of said tually adjacent ends of the drums.

shoulders cannot cause material variations in the amount of energizing surface contact at either end 5 fi wes Cite in e fi 0 thlS patent of the spring and are not apt to cause axial bind- ITE STATES P T NT ing of the spring between said shoulders.

Number Name Date 1, wfirei fhetitfify fiftld23322235112;23 1,984,297 Aben 11, 1934 2,481,248 Schneider Sept. 6, 1949 is offset axially of the spring toward one of the 10 

